TISSUES– Groups of cells with similar structure and function
– Four primary types
• Epithelial tissue (epithelium)
• Connective tissue
• Muscle tissue
• Nervous tissue
Epithelial Tissues• Locations
– Body coverings
– Body linings
– Glandular tissue
• Functions
– Protection
– Absorption
– Filtration
– Secretion
• Cells fit closely together and often form sheets
• The apical surface is the free surface of the tissue
• The lower surface of the epithelium rests on a basement membrane
• Avascular (no blood supply)
• Regenerate easily if well nourished
Classification of Epithelia• Number of cell layers
– Simple—one layer
– Stratified—more than one layer
• Shape of cells
– Squamous• flattened
– Cuboidal• cube-shaped
– Columnar• column-like
Simple Epithelia• Simple squamous
– Single layer of flat cells
– Usually forms membranes
• Lines body cavities
• Lines lungs and capillaries
• Simple cuboidal
– Single layer of cube-like cells
– Common in glands and their ducts
– Forms walls of kidney tubules
– Covers the ovaries
• Simple columnar
– Single layer of tall cells
– Often includes mucus-producing goblet cells
– Lines digestive tract
Stratified Epithelia• Stratified squamous
– Cells at the apical surface are flattened
– Found as a protective covering where friction is common
– Locations• Skin
• Mouth
• Esophagus
• Stratified cuboidal—two layers of cuboidal cells
• Stratified columnar—surface cells are columnar, cells underneath vary in size and shape
• Stratified cuboidal and columnar
– Rare in human body
– Found mainly in ducts of large glands
• Pseudostratified columnar
– Single layer, but some cells are shorter than others
– Often looks like a double layer of cells
– Sometimes ciliated, such as in the respiratory tract
– May function in absorption or secretion
• Transitional epithelium
– Shape of cells depends upon the amount of stretching
– Lines organs of the urinary system
Glandular Epithelium• Gland
– One or more cells responsible for secreting a particular product
• Two major gland types
– Endocrine gland
• Ductless since secretions diffuse into blood vessels
• All secretions are hormones
– Exocrine gland
• Secretions empty through ducts to the epithelial surface
• Include sweat and oil glands
Connective Tissue
• Found everywhere in the body
• Includes the most abundant and widely distributed tissues
• Functions
– Binds body tissues together
– Supports the body
– Provides protection
• Extracellular matrix
– Non-living material that surrounds living cells
Connective Tissue Types
• Bone (osseous tissue)
– Composed of
• Bone cells in lacunae (cavities)
• Hard matrix of calcium salts
• Large numbers of collagen fibers
– Used to protect and support the body
• Hyaline cartilage
– Most common type of cartilage
– Composed of
• Abundant collagen fibers
• Rubbery matrix
– Locations
• Larynx
• Entire fetal skeleton prior to birth
• Elastic cartilage– Provides elasticity
– Location• Supports the external ear
• Fibrocartilage– Highly compressible
– Location• Forms cushion-like discs between vertebrae
• Dense connective tissue (dense fibrous tissue)
– Main matrix element is collagen fiber
– Fibroblasts are cells that make fibers
– Locations
• Tendons—attach skeletal muscle to bone
• Ligaments—attach bone to bone at joints
• Dermis—lower layers of the skin
• Loose connective tissue types
– Areolar tissue
• Most widely distributed connective tissue
• Soft, pliable tissue like “cobwebs”
• Functions as a packing tissue
• Contains all fiber types
• Can soak up excess fluid (causes edema)
– Adipose tissue
• Matrix is an areolar tissue in which fat globules predominate
• Many cells contain large lipid deposits
• Functions– Insulates the body
– Protects some organs
– Serves as a site of fuel storage
– Reticular connective tissue
• Delicate network of interwoven fibers
• Forms stroma (internal supporting network) of lymphoid organs
– Lymph nodes
– Spleen
– Bone marrow
• Blood (vascular tissue)
– Blood cells surrounded by fluid matrix called blood plasma
– Fibers are visible during clotting
– Functions as the transport vehicle for materials
Muscle Tissue
• Function is to produce movement
• Three types
– Skeletal muscle
– Cardiac muscle
– Smooth muscle
• Skeletal muscle
– Under voluntary control
– Contracts to pull on bones or skin
– Produces gross body movements or facial expressions
– Characteristics of skeletal muscle cells
• Striated
• Multinucleate (more than one nucleus)
• Long, cylindrical
• Cardiac muscle
– Under involuntary control
– Found only in the heart
– Function is to pump blood
– Characteristics of cardiac muscle cells
• Cells are attached to other cardiac muscle cells at intercalated disks
• Striated
• One nucleus per cell
• Smooth muscle
– Under involuntary muscle
– Found in walls of hollow organs such as stomach, uterus, and blood vessels
– Characteristics of smooth muscle cells
• No visible striations
• One nucleus per cell
• Spindle-shaped cells
Nervous Tissue
• Composed of neurons and nerve support cells
• Function is to send impulses to other areas of the body
– Irritability -Conductivity
Tissue Repair (Wound Healing)• Determination of method
– Type of tissue damaged
– Severity of the injury
A. Regeneration
– Replacement of destroyed tissue by the same kind of cells
B. Fibrosis
– Repair by dense (fibrous) connective tissue (scar tissue)
Events in Tissue Repair• Capillaries become very permeable
– Introduce clotting proteins
– A clot walls off the injured area
• Formation of granulation tissue
– Growth of new capillaries
– Rebuild collagen fibers
• Regeneration of surface epithelium
– Scab detaches
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